Damage from fatigue that can result in product failure if the extent of damage is undetected. Historically, several factors have complicated inspection of fatigue damage in components. For example, physical, traditionally-measurable defects are not formed until well over 50% of the fatigue life is used. At first, the physical defects that do form are very minute. Eventually, the defects grow to an easily-measured size only near the very end of the life cycle when failure becomes eminent. Inspection is also complicated because technicians must first know where to expect fatigue to occur and must then inspect that location or area to look for fatigue damage, such as a growing fatigue crack.
The most prevalent, nondestructive test techniques (NDT) used for surface examination of fatigue include magnetic particle inspection (MPI) and liquid penetrant inspection (LPI). These techniques cannot be used or are not effective in many cases. For instance, a minimum defect size for some components may usually be in the range of about 0.030″ or 0.8 microns. The inspection codes for these prevalent test techniques, however, typically consider a minimum size of a relevant defect as being in the range of 0.063″ or 1.6 microns. These surface NDT techniques will not reveal indications less than about 0.030″ or 0.8 microns. Unfortunately, this means that an actual fatigue crack in a component would only reach the detectable level of these techniques after over 95% of the fatigue life has already passed. As such, these prevalent test techniques would only detect the defect when fatigue failure is close at hand.
In contrast to the prevalent test techniques, eddy current techniques are now available for fatigue inspection. One of the eddy current techniques available is Meandering Winding Magnetometer (MWM) with a multi-frequency scanning eddy current sensor. In proving out of fatigue cracks during the life cycle using this particular eddy current technique on a component, a fatigue crack was observed at the 50% of life range. This observed fatigue crack was not detectable with the MPI and LPI techniques, but was verified via surface examination using a scanning electron microscope (SEM). This same crack was finally detected with the MPI and LPI techniques at a length of about 0.030″ at an estimated 95% of the fatigue life used (5% remaining life).
Although these eddy current techniques have some value, they still have some limitations. For example, these eddy current techniques can generally detect fatigue damage at some level in the 30-50% range of the used fatigue life of a component. Yet, wear and mechanical damage of the component tends to introduce more scatter in the results in the eddy current techniques. The introduced scatter of the results interferes with an assessment of the remaining fatigue life of the component. This may be the case where the nondestructive technique works to a large degree, but may prove difficult to actually use in real life applications.
In contrast to the above techniques, it is known that X-ray can be used to measure changes in the strain of a component associated with fatigue damage. The use of strain measured by X-ray to predict fatigue damage level (or status or life) was proposed in 1990, as can be found in the disclosure of SU 1718068. The technology was at least partly defined in this disclosure, but was apparently never put into practice. In fact, even practical aspects of applying X-ray strain measurements to determine fatigue damage level (or life used/remaining) are not disclosed in SU 1718068.
In the X-ray technique of SU 1718068, the life of a component is estimated using micro-strains ε and their dispersion D. Critical values of the micro-strain εcr and the dispersion Dcr are determined according to X-ray measurement results. Maximum critical values εmaxcr and Dmaxcr are determined by means of X-ray measurement of a controlled specimen at various surface points. After that, the number of Ni cycles for the specimen's lifetime is determined using a constraint equation. Then, the probability of failure is estimated, and the material lifetime is determined.
The X-ray technique of SU 1718068 has a number of practical disadvantages. First, the technique only uses two parameters (micro-strain and dispersion), which may not give accurate estimates. Second, it is not possible to use the X-ray technique of SU 1718068 without also using an older technique to actually make estimations for real components. For instance, realizing the X-ray technique of SU 1718068 requires using reference samples or requires actually cutting the samples (i.e., destruction of the samples) to achieve measurements. This leads to decreasing accuracy and utility of the technique's estimations. Finally, the X-ray technique of SU 1718068 is not suited for estimating the relative point where the measured component is actually located along a span of fatigue.
The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.